Fuel cells are devices which extract electrical energy due to an electrochemical reaction occurring in an electrolyte membrane, and some fuel cells need the electrolyte membrane to be humidified in order to generate power. In general, pure water is used to humidify the electrolyte membrane so that impurities do not adhere to the electrolyte membrane and cause the performance of the fuel cell to deteriorate. Pure water is also used to cool the fuel cell. However, when pure water is used for humidifying or cooling the electrolyte membrane, if the system is left below freezing point when the fuel cell has stopped, the water freezes inside the system, and there is a possibility that the internal structure of the system may be damaged due to the volume expansion caused by solidification. There is also a possibility that due to the frozen water, the flowpaths which supply gas, air or water to the fuel cell may also become clogged so that the system cannot be restarted.
To resolve these problems, JP7-169476A published by the Japanese Patent Office in 1995 discloses a method for warming the fuel cell with a heater so that its temperature does not fall below 0° C. when the fuel cell has stopped. Also, JP8-273689A published by the Japanese Patent Office in 1996 discloses a method of avoiding freezing of the water in the fuel cell by discharging water outside the fuel cell when the fuel cell has stopped, thus causing the water to freeze outside the fuel cell.